Functional poly(phenylacetylene)s carrying azobenzene pendants: Polymer synthesis, photoisomerization behaviors, and liquid-crystalline property

Functional poly(phenylacetylene)s (PPAs) bearing different azobenzene pendants were synthesized in desirable yields and molecular weight by using organorhodium complexes [Rh(diene)Cl]2 as catalysts. The structure of the derived azobenzene-functionalized PPAs was characterized by NMR, IR, and UV spectroscopic techniques. Their photoinduced isomerization behavior was monitored with UV-visible spectroscopy. The thermal stability was evaluated by TGA technique. Polarized optical microscope (POM) observations indicated that the PPAs constructed by linking azobenzene moieties via a longer flexible alkyl spacer to PPA backbone showed typical liquid-crystalline property and the mesophase was assigned to SmA phase. Their phase transition behaviors were further investigated by differential scanning calorimetric (DSC) measurements. The molecular packing modes were analyzed by using X-ray diffraction (XRD) measurement and theoretical simulation. These results revealed some details about the interactions between the polymer backbone, flexible alkyl spacer, and azobenzene functional moiety, which are constructive to design and synthesize novel functional conjugated polymers.